Our research projects using TLS

We have diverse research projects that take advantage of the terrestrial lidar capabilities. These include:

Modeling multipath error in GPS measurements

People: Marcelo Santillan, Tim Melbourne, CWU

The PANGA GPS station on Manastash Ridge and the observatory, which is the primary source of multipath error (photo by Anne Egger).

One of the largest sources of error in high-rate (1-second vs. 24-hour) GNSS positioning is satellite signal multipath, in which the transmitted satellite signal takes an indirect path to the receiver, usually via reflections off nearby structures. For daily measurements, multipath mostly averages out during the 24-hour observation period, but with high-rate estimations multipath can contribute up to 10 cm of apparent motion. Fortunately, satellite geometry in the sky repeats every sidereal day, so multipath, which depends on satellite geometry, also repeats and many techniques exist to average and difference sidereal days to minimize multipath-induced error. However, because multipath manifests itself as geometry-dependent perturbations to the range and carrier-phase measurements recorded by the GNSS receiver, it should be possible to explicitly model the satellite signal reflections if one knows the satellite orbits (known) as well as the local 3D geometry of the near-receiver topography. Utilizing TLS, we will produce a detailed 3D model of two of the noisiest site locations (those on Lind Hall and Manastash Ridge), and then use these models in forward-modeling multipath error.

Sediment migration on the Elwha River

People: Lisa Ely, CWU; Andy Ritchie, USGS

TLS in the partially-drained Mills Lake reservoir above the upstream dam on the Elwha River (photo by Lisa Ely)

The Elwha River on the Olympic Peninsula in Washington State is an important salmon spawning grounds as well as a major source of sediment to the shoreline. But salmon spawning and sediment transport have been hindered by the presence of two dams along the river. Those dams are now in the process of being removed, exposing sediments that were deposited in the reservoirs. Using TLS, we will monitor the volume of sediment that is being removed from reservoir delta deposits over time.

More information about the USGS Science to Support the Elwha River Restoration Project

Offset alluvial channels along the White Mountains Fault, Chalfant Valley, CA

People: Zach Lifton, Georgia Tech; Jeff Lee, CWU

Rex Flake working at the TLS station in the White Mountain Fault study area (photo by Zach Lifton)

The western side of the White Mountains exposes a fault zone that preserves geomorphic evidence for dextral and normal slip. Offset and beheaded stream channels, cut into alluvial fan deposits, provide spectacular visual documentation for progressive dextral offset along the White Mountains fault zone. Stream channels show dextral offset that ranges from ~500 m to ~9 m. Using the TLS, we will map fault scarps and offset channels and calculate an accurate magnitude of offset. Combining the offset measurements with ages for the offset channels will provide a Pleistocene to Holocene dextral slip rate along this fault.

Mapping paleoshorelines and fault displacement in Surprise Valley, CA

People: Anne Egger, CWU

The TLS scanner set up in Surprise Valley, CA, with subtle paleolake shoreline features and a target in the distance (photo by Anne Egger).

In seismically active regions with long earthquake recurrence intervals, such as the northwestern Basin and Range, multiple techniques need to be applied to ascertain the paleoseismology of a fault system and thus the seismic hazard. The Surprise Valley fault in northeastern California has been trenched to study its paleoseismicity (see Personius et al., 2009, for trenching results), but it is not the only fault in the region. Numerous smaller-offset normal faults also have the potential to rupture, and their paleoseismicity has not been determined. Terrestrial lidar is being used to determine the Pleistocene-to-recent activity along these faults through high-resolution imaging of paleoshorelines of pluvial lakes on different fault blocks. Lidar data will be used to generate digital elevation models on which paleoshoreline features can be mapped, correlated, and analyzed for offset and deformation.